circuit theory 1 notes, Slides of Circuit Theory

Download circuit theory 1 notes and more Slides Circuit Theory in PDF only on Docsity! BASIC CONCEPTS PROF. DR. MUSTAFA K. UYGUROGLU ELECTRIC CIRCUIT • An electric circuit is an interconnection of electrical elements. SYSTEMS OF UNITS Quantity Basic Unit Symbol Length meter m Mass kilogram kg Time second s Electric current ampere A Thermodynamic Temperature kelvin K Luminous intensity candela cd THE SI PREFIXES • Prefixes on SI units allow for easy relationships between large and small values CHARGE • Charge is a basic SI unit, measured in Coulombs (C) • Charge of single electron is 1.602*10-19 C • One Coulomb is quite large, 6.24*1018 electrons. ELECTRIC CURRENT • Current, i, is measured as charge moved per unit time through an element. • Unit is Ampere (A), is one Coulomb/second dt dq i  DC VS. AC • A current that remains constant with time is called Direct Current (DC) • Such current is represented by the capital I, time varying current uses the lowercase, i. • A common source of DC is a battery. • A current that varies sinusoidally with time is called Alternating Current (AC) • Mains power is an example of AC 11 DIRECTION OF CURRENT • The sign of the current indicates the direction in which the charge is moving with reference to the direction of interest we define. • We need not use the direction that the charge moves in as our reference, and often have no choice in the matter. 12 VOLTAGE II • It is equal to the energy needed to move a unit charge between the locations. • Positive charge moving from a higher potential to a lower yields energy. • Moving from negative to positive requires energy. 15 POWER • Power: time rate of expending or absorbing energy • Denoted by p • Circuit Elements that absorb power have a positive value of p • Circuit Elements that produce power have a negative value of p dw p p vi dt   ENERGY e Law of Conservation of Energy: the net power absorbed by a circuit is equal to 0. In other words, the total energy produced in a circuit is equal to the total energy absorbed e Energy: capacity to do work, measured in joules (J) t SF w= | pdt= | (+vi) dt t 0 to If current and voltage are constant (DC), + w= | pdt = p(t — to) t 40  PSC: EXAMPLE II Find the power (absorbed) for each device. 2A 4— 4V 2A<4— + AV 2A—> + AV 2A—r av  PSC: EXAMPLE III Find the total power developed in the circuit. Voltage Current | Power a) (A) | (W) a -18 -51 b -18 45 c 2 -6 d 20 -20 é 16 -14 f 36 31 oe CIRCUIT ELEMENTS • Ideal Independent Source: provides a specified voltage or current that is completely independent of other circuit variables • Ideal Independent Voltage Source: